Apparatus for controlling rectified voltage



\Oct. 2, 1951 s JR 2,569,698

APPARATUS FOR CONTROLLING RECTIFIED VOLTAGE 7 Filed March 5, 1947 3 Sheets-Sheet l 1951 F. H. SHEPARD, JR 2,569,698

' APPARATUS FOR CONTROLLING RECTIFIED VOLTAGE Filed March 5, 1947 3 Sheets-Sheet 2 Patented Oct. 2, 1951 UNITED O F CE rArrARArUsnon oomrnoi piiyjd REGTIEI LMGE Francis Shepard, J 1'); Madison; N. J Applicationc at a, 1 7,;SQri 1N 7.32.066

Y recl i s. (01321- 48) 1 My; i ve ion .relate a m d. a d ppa atus for controlling voltage andmore particularly to am an apparatus f PIQQWmaJ W F low. impedance, a variable unidirectional voltage .of controllable sign or polarityand amplitude in aqsimple, expeditious and,convenient manner.

:My method and apparatus can transform electric. .powenfrom alternating current .to direct current or may-.-tr;ansform direct current toalternating current in, a gsimple .and; eflicient,manner. .lnthe prior art variable direct voltage current from an alternatinggcurrent source ;;is obtained largely by theruse :of, such instrumentalities, as the thyratron, .theignitron or the amplidyne. Thesedevices .are costly and. cumbersome. The

thyratronn and. ignitron .are essentially unidiauntiLthe positive voltageand current through them arereduced to zero. They cannot be .used

toopen. a circuit "carrying, current. Although they. are .in themselves low impedance devices,

they normally conduct only a fraction of. the. time, 7

hencethe impedance they present to the, load is that of. the supply :divided by. the total timeover thezconduction time. Since they will conduct current inone direction only, they will not .hold down .on. overriding voltage (1; e. dynamically brake or damp amotor they .may .be driving).

The amplidyne is not only costly but is heavy and "itsresponseis sluggishsothat there is a tendency v.to. produce a'lag.

'.' One..0bj.Ct ofomy invention is to .provide; a

amplitude which isrelatively light in weight.

Another object .of my invention is to produce avariable-voltage source which is inexpensive in construction and efiicient in operation.

'Another object of my invention is to provide a low impedance, variable unidirectionalvoltage .source which is fast inresponse and simple to construct.

, Other and further objects-of my invention will appear from the following description.

/ In general. my invention contemplates the controlled transformation of power infan .efiicient v means. and-method. of producing a variable unidirectional voltage of controllable polarity ,and

A further object of.my inventionis to provide .low impedance variable unidirectional voltage source of controllablepolarity and amplitude using a vibrating contact relay, wherein current ,may fiowr in both directions, andis hence inher- .50 .ently efiective in damping its load.

al e nat g-r tipo er ,multiple, relays,..;using on 'fo re'ac" and simple manner, from; alternating current to iiet 3 m and Irwi @i wt -urre i erhating currentby improvd"circuits employing, a yibratlngcontact.relay. My sys temf is admirably edMfifliipnusfe i fap j f l s f onv t inverter and'in controlequip ntgsuch as'battery elwr rs. igen tet r fi ld. w e r. c n ro l u inatio 91 -i en re ?e' i .fi i rli leqi 1 in .e efl ael anth m?- l mnsr t lemiemb e t r t a 9. 19 o iret ..u n ql e e i, an des e lu frqmmax mnmin i eit e ll i rd .l am ximu inosit ro e a si ia w wepha e ttl e atiQe tt eml v.w Y Th Yalu sofi them .inii me .ir t q r re t' l ee wi11.be..e u .i .hee atine tu re v lta e app edto t e re a ;,rontec sta liea (o anle .leragin typemeter. res s ance, t dir current source-w ihee ua t heimne lanc o theaalter ati ;fillrrfl rsmlp adde .v te l tqthedirectcurrent; resistance of the filter choke and ,tne..,. commutatin ..res sto Th .nurre Whiche will; ,flow.;in-. the; dire t. current. .IBSiSEQQF .load vwillobe equal to ethe voltage to hich .the source.isisetyidivided byithe; source plus t e loa resistances.

. If a.: di-rectl current; .voltaee; such as. a. batt r .or; the 1hack.elect.romotive;force, .of a motor exists .inthe load,.-.,the currentwiu bewequal tothesourc voltage less the.;load. v,oltage. divided Joy the load plus the,.,source.;resistance ..:;If'.-.;t el.l ad volta .should exceed..the. sgurce..vgltage,; the current will .reverse. and. c0.w 1t'w e;;fed. romrt ire cur.re,nt ,load to jgh ing current supply. .Ih sunu u l charac e rqie fiatve e whe .my..,meth d. end ap ara us ar ap lie I n-t control of devices having direct current motors. I emfi ms-enabl d rnemieel rfiqbre t ei cur nt'mo o s-aeiwe aet lere d et rever e. a d .re e zthem ate i $29 i o i'z r t ful s ee th r d r ti e .ii mn .taml incurr n .ih ..ne siW. id n la eememit isiet eiheme ;in ntr rheostats.

r' I am f urther enabled to i ernploy polyphase In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith, and in which like reference numerals are used to indicate like parts in the various views:

Figure 1 is a diagrammatic view of a circuit capable of carrying out the method and embodying the apparatus of my invention.

Figure 2 is a diagrammatic view of anothed circuit capable of carrying out the method and embodying the apparatus of my invention.

Figure 3 is a view of a circuit showing another form of apparatus capable of carrying out my method and embodying the apparatus of my invention and employing a saturable reactor in the circuit.

Figure 4 is a diagrammatic view showing my method and apparatus applied as an inverter to produce an alternating current output from a direct current input.

Figure 5 is a series of curves of voltage plotted against time illustrating the action of my method and apparatus.

Figure 6 is a diagrammatic view showing the construction of a relay suitable for use in carrying out my invention.

Referring now to Figure 1, the output of an alternating current source I of any suitable frequency and voltage is impressed across the primary winding 2 of a transformer 3. The ends of secondary winding 4 are connected by conductors 5 and 6 to contact points and 8 of a vibrating contact relay 9 through commutating resistors l and H. The relay 9 may be of any suitable type. A relay manufactured by the Western Electric Company under the identification D-1684'79 is especially suitable for use in my method and apparatus. The relay is polarized, as can be seen by reference to Figure 1. The controlled polarizing current is supplied to the coil l2 from a battery l3 through conductors l4 and I and I9, and variable resistor l6. Alternatively, the vibrating contact may be given magnetic polarity by including it in a magnetic flux path in any suitable manner known to the art.

Referring now to Figure 6, a core 205, made of magnetic material, carries a winding H2 and a winding 2|9. The vibrating armature 2H, which is adapted to make contact with stationary contact points and 208, is flexibly mounted from the core 205 in any appropriate manner as, for example, by flexible connection 220. A D.-C. polarizing current may be passed through terminals 201 and 202 and the relay exciting current may be passed through terminals 203 and 204. If desired, the D.-C. polarizing current may be passed through terminals 203 and 204 while the signal currents may be passed through terminals 20| and 202.

It is to be understood that the showing of the relay is diagrammatic and illustrative only and that any suitable relay may be employed. It is preferable to use a relay armature which has no return spring such as shown in Figure 6, thus making the relay entirely aperiodic and enabling nected in parallel with the secondary winding 4. The upper end of the coil 12 is connected to a point between capacitor 2| and resistor 22 by means of conductor 23 and variable capacitor 24. The capacitor 24 isolates the battery |3 from the alternating current power supply and prevents its being short-circuited. The value of the capacitor 24 may be varied to determine the initial phase setting.

One direct current output terminal 25 is connected to the midpoint of the secondary winding 4 by conductors 26, I5 and 20. The other direct current ouput terminal 21 is connected to the vibrating contact through conductor 28 and choke coil 28 which filters and smooths the direct current output. A capacitor 30 and a capacitor 3| are connected in parallel with the contacts and 8 to bypass transients and suppress sparking.

The operation of the apparatus shown in Fi ure 1 and my method can best be understood by reference to Figure 5 in conjunction with Figure 1. The curve A represents the alternating voltage occurring at the upper contact I which is connected to the upper end of the secondary winding 4. The curve B represents the voltage occurring at the lower contact 8 of the relay which is connected to the lower end of the secondary winding 4. In the curves it has been assumed that the relay has a negligible transfer time. Actually the relay has a very small transfer time. It is sufficiently small as to be negligible so that the curves represent what actually occurs for all practical purposes.

Referring to Figure 1, the potential of the point, connecting condenser 2| and resistor 22 with respect to the center tap of secondary winding 4, is a relatively constant A.-C. value which can be rotated in phase by the adjustment of resistor 22. Adjustment of condenser 24 will change the phase of the current passed through condenser 24 and coil |2 with respect to the voltage across them. Setting the value of condenser 24 can be used to make the relay phase correct for maximum and minimum settings of resistor 22.

Let us now assume that the upper end of secondary winding 4 is going positive. A transient voltage will be impressed from the upper end of winding 4 through the capacitor 2| through the capacitor 24 through the winding |2 through the conductors l5 and 20 to the mid-tap of the winding 4. A transient voltage will also be impressed from the mid-tap of winding 4 through conductors 20 and I5 through the winding l2 through conductor |4 through conductor 23 through capacitor 24 through resistor 22 to the other side of the winding 4. It will be observed that the direction of the voltage from the upper end of the winding 4 opposes the direction of the voltage from the mid-tap of winding 4 to the lower end thereof. The voltage impressed across the winding 4 is through capacitors so that the voltage will lead the current. The voltage in the opposite direction is impressed from the mid-tap of the winding 4 to the lower end of the winding through a variable resistor 22. This voltage will be more in phase with the current flowing through winding l2. In other words, the voltage drop through the capacitor 2| and the voltage drop through the resistor 22 will equal the voltage across the winding 4. The reduction of the IR, drop across the resistor 22 will increase the voltage drop due to the capacitive impedance of the capacitor 2|. Similarly an increase of the IR drop across the resistor 22 will decrease the capacitive impedance shifting network comprising a capacitor 36 analogous to capacitor 21 in Figure l and a resistor 3'! analogous to the resistor 22 in Figure 1. The network comprising resistor 32 and capacitor 33 is a phase limiting control for point 35. The network comprising capacitor 50 and resistor is a phase limiting control for point 34. The variable resistor 37 is a phase shifting control for governing the amplitude and polarity of the output voltage. The anode 38 of a thermionic tube 39 is connected to the positive terminal of the battery l3 through control coil I2 and the conductors l4 and 48. A screen grid 4| is connected to a voltage divider 42 by variable arm 43. The screen grid acts as a polarization control. The control grid 44 of the thermionic tube is connected to a point between capacitor 36 and variable resistor 3'! by conductor 23 and capacitor 24. The cathode 45 of the tube 39 is connected to the mid-point of secondary winding 4 through conductor 46.

The operation of the circuit as shown in Figure 2 is essentially the same as that shown in Figure 1. I am enabled, however, to use much lighter phasing equipment. The value of the current flowing through control coil l2 of the relay 9 is governed by the potential applied to the control grid 44. This is represented by the IR drop across resistor 52. When the resistance of control resistor 3'1 is at a maximum, the phasing current in control coil [2 will be such that the contacts will be in phase with the voltage across secondary winding 4 and the voltage across output terminals 27 and 25 will be at a maximum amplitude. When the resistance across control resistor 31 is at a minimum, the current flowing through coil 12 will be approximately 180 out of phase with the voltage across secondary winding 4 and the voltage across output terminals 21 and 25 will again be at a maximum amplitude but of opposite polarity. By means of my phase limit control circuits, I am enabled to obtain a shift of more than 180 by adjustments of capacitors 50 and 33 and adjustments of resistors 32 and 5|.

Referring now to Figure 3, there is shown another form of apparatus embodying and capable of carrying out the method of my invention in which a saturable reactor is used to govern the phase of the control current through coil l2 of the relay. A saturable reactor indicated generally by the reference numeral 60 has a winding Bl connected in series with a resistor 62 across the transformer secondary 4. The control coil I! of the relay is connected across the resistor 62 and the IR drop across this resistor will govern the current flowing through the coil I2. A capacitor 63 is placed in the circuit to govern the initial phase set. The control winding 64 of the saturable reactor is connected in series with a thermionic tube 65; the winding 64 and the tube 65 being connected across the secondary winding 4 by means of conductors 56 and 51. The phase of the current flowing through the control coil I2 is governed by the phase of the current flowing through the resistor 62. This in turn is governed by the current flowing through the circuit including the resistor 62 and the winding 6!. The IX drop through winding GI and the IR drop through resistor 62 will equal the voltage across the secondary winding 4. The phase of the current flowing through the inductanceresistance phase shifting circuit will depend on the relative values of the inductance and the resistance. A variation of the value of the inductance of the winding Bl will shift the phase of the current flowing through the resistor 52 and hence through the control winding 12 of the relay 9. When the current flowing through winding 64 is of high value, the core becomes saturated and inductance of the winding 6| is at a minimum. When this condition prevails the control current [2 will be in phase with the voltage developed across the secondary winding 4 and the circuit is such that when the upper portion of secondary winding is going positive the armature I! of the relay will make contact with stationary contact point 1 so that the direct current output terminal 21 will be of posiive polarity. Furthermore, when the control current l2 of the relay is exactly in phase with the voltage developed across the transformer secondary 4, the output voltage will be of maximum amplitude.

I provide a current path comprising capacitor 14 and the thermionic tube 65 across the upper branch of secondary winding 4. When conductor 5 is of positive polarity current will flow from conductor 5, through capacitor 14, through the plate to cathode circuit of the tube 65, through conductor 66 to the mid-tap of the secondary winding 4, thus charging the condenser 14. It will be observed that the lower plate of the capacitor I4 is always negative with respect to the upper plate and hence with respect to conductor 5. The control winding 64 of the saturable reactor is connected across the capacitor 14 so that the integrated charge of the condenser 14 will represent the integrated current flowing through the control winding 64. A permanent magnet shown diagrammatically and indicated by the ref erence numeral 12 is provided for polarizing the relay.

The condition of maximum current through the control winding 64 of the saturable reactor is brought about by impressing a high positive potential at control terminal 10 with respect to control terminal ll during the time that the plate 16 of tube 65 is positive. This permits maximum current to flow from plate to cathode impressing a maximum charge on condenser 14.

I use a capacitor of large capacity such as an electrolytic condenser, whereby during the half cycle when the upper point of secondary winding 4 is of negative polarity, the charge of the condenser will be sufllcient to permit current to flow through the control winding 64 during this half cycle. On the next half cycle the condenser becomes charged again and current continues to flow through the winding 64 of the saturable reactor 60, at a value governed by the potential applied to the control grid 13.

Any suitable means for controlling the voltage across control terminals 10 and "H may be employed. When this voltage is such that the grid is highly negative with respect to cathode, during the time conductor 5 is positive, the resistance of the thermionic tube will be increased to such point that it will become a non-conductor. When this point is reached, no charging current will flow through the capacitor 14 and hence no current will flow through the winding 54 of the saturable reactor and maximum inductance of winding BI will be effective. When this condition prevails, maximum IX drop will appear across the reactor, the current will be a minimum, and the voltage across the output terminals 21 and 25 will be again of maximum amplitude but out of phase with the voltage across the secondary winding 4. In other words, when the upper portion of secondary winding 4 is at its maximum positive value, the voltage at terminal; 21. will beof. maximum negative polarity.

Complete control. of the. entire. range is easily,

exercised. by, controlling. the, voltage acrosscontrolterminals I and ML. is .the same .as that. heretofore. described. and illustrated. in. Figure. 5.. different. phase. control. network is used. to. accomplish. thev same results.

and the circuit. shown in. Figure 3. is. another em.- bodiment. of my invention.

Referring now to-Eigure. 4,, I have shown. a.

Oneof the-advan.--

ticn. of mymethod andapparatus tov thed'ynamic'.

braking of direct. current. motors. and their. ac.- celeration, deceleration and. reversal.

This characteristic may. be. employed to provide an. alternating current. power. supply from:

a... direct current. source, such.- as a battermior the operation, of. alternating, current equipment.

of all types and descriptions.

Asource of direct. current. potential is applied across terminals 80'. and.8l.. A pair of" polarized relays 82. and 8 3are employed, of they type similar, to that describedhereinabove.

conductor 84' bythe conductor 8]. Contact point 88 of -the relay 83 is connected to. the conductor 8 l'by. the conductor 89'. The other. terminal of the direct current .input'potential 8Iis. connected, to. a conductor. 90. The other'stationary"contact- 9I'of the relay 82is connected. by conductor'92 to the conductor 90; The otherstationary contact 93"ofthe relay'83 is connected'loyv conductor 84: to the conductor 90. Thecontrol-winding 95 of therelay 82' and the control*winding 96 of the relay 8.3 are connected in. series by-a conductor. 91. The other end of control winding 95 is connected byconductors I08 and I0! to the moving contact 98' of the relay 82. The other end of the winding 96 is connected by conductor 9'9, resistor I00andconductor' IM to the moving contact 1020f therelay 83'. Conductors 99 and I05 are inter-connected by a capacitor I 83, the value of "which sets the output frequency. The resistor I00; if desired,- may be a choke coil in order to obtain better frequency stability.

Polarizing coils 95 and-96 connected across the- D'r-G. input areprovided; 'I'hecurrent flowing through thepolarizing coils isgoverned by the variable resistor I 6 In operation, letus assume the armatures 98' and I02 of therelays 82 and 83" are in the positionshown in-Figure- Current will flow from terminal 80 through the choke coil 85, through the conductor- 81; through" the. conductor I0],

through the control winding 95201" the relay 82;,

through conductor 9I-;.thro;ugh.the control winding: BZof the relay. 83;.through the. conductor 99,, through the-resistorl00, through conductor IOI,,

through armature. I02; through; conductor 94, through conductor 90? and thence to the other terminal 8| of the direct; current source. Glil'giZ&i3iOl1;0f'thBlCOlltlOl windings 95 and 96 causes. the armatures 98.and I02. of the polarized relays 82. and .83 to shift so. that contact will be.

made by armature. 98 .withcontact point 9| and by armature I82 with contact point. 88.

During-the. flow of current just described, that is; with armature 98. in, contact with contact.

point 8.6.andarmature I02. in contact with contact point. 93., alternating current. output terminal ma-.was..the. same polarity asdirect our.

The principle. involved This.-

One terminal. 80 ofthe directcurrent source is connected to a. conductor. 84 through choke and filter coil 85.. OhecOntact 86 of relay 82 is connected to the The rent potential terminal 80, Similarly, alternatchoke coil 85, through conductor 89 to contact It will be observed point 88' to armature I02; that alternating current output terminal I09 is now connected with opposite polarity. The circuit is completed through conductor IOI, through resistor I0.0,.througl1 conductor 99, through control winding 98- of" relay 83, through conductor 91., through control winding of relay 82-, through conductor I06, conductor I01, through armature 98, through contact point 9|, conductor 92' to the other direct current terminal 8I.

The shifting of the relay armatures does not instantaneously shift the voltage across alternating current terminals I08 and I09 due to the effect of the capacity of the-network. The-fre-- quency of the output alternating current will depend upon the value of the capacitor I03 and it may be adjusted to obtain any desiredfrequency.

It is to be understood that the above circuits are given by way of illustration and not byway of limitation and that my method and apparatus aresusceptible of many applications within the spirit of my invention. As will be readily understood by those skilled in the art, three relays in. parallel may be employed to convert three-phase input power to a direct current output. In such case, the ripple is greatly reduced. In the circuit three power transformers may be employed in which one primary is connected across the first and second line. One primary is connected across the first and third line and one primary is con.- nected across the first two primarywindings;

The secondaries of eaohof'the transformers are connected to the stationary contacts of the relay'as' shown in Figure 1.

My method and apparatus similarly may be used for power interchange between two nonsynchronous alternating current systems.

It will be seen that I have accomplished theobjects of my invention. I provide a method and apparatus for inter-transforming electric power from alternatin current to direct current or vice" versa in a simple and efiicient manner. I have avoided the use of costly and cumbersome de vices such as the thyratron, the ignitron or the amplidyne'. I'have provided a means-and method of producing a variable unidirectional voltage of controllable polarity and amplitude which is light in weight, inexpensive in construction and ethcient inoperation. I have made available to the art alow impedance variable unidirectional voltage'source which is fast in response andsimple to construct. ILhave provided an apparatusemploy ing av vibrating contact relay in whichcurrent may flow inboth directions and which is hence inherently elfective in damping the output load;

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to, other features and sub-combinations. This is contemplated by'and is within the scope of my claims. It is further obvious that various changes may be made indetails within the scope of my claims without. de-

parting from the spirit. of my invention. It is thereforeunderstood that my invention is not to 11 be limited to the specific details shown and described.

Having thus described my invention, I claim:

1. Apparatus for inter-converting alternating current to an output current havin a direct current component including in combination a relay having a pair of stationary contacts and a vibrating contact adapted to make alternate connection with the stationary contacts, means for supplying alternating potential to the stationary contacts, means including the vibrating contact for removing direct current, a choke coil connected in series on the output side of the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential, phase-shifting means for shifting the phase between the vibration of the vibrating contact and the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a network having a capacitor and a resistor in series and means for varying the relative value of the resistance of the resistor with respect to the capacity of the capacitor.

27 Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a relay having a pair of stationary contacts and a vibrating contact adapted to make alternate connection with the stationary contacts, means for supplying alternating potential to the stationary contacts, means including the vibrating contact for removing direct current, a choke coil connected in series on the output side of the 1 vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential, phase-shifting means for shifting the phase between the vibration of the vibrating contact and the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a network having a first resistor and capacitor in series, a second resistor and capacitor in series and a third resistor and capacitor in series, the third resistor and capacitor being connected across a point between the first resistor and capacitor and a point between the second resistor and capacitor.

3. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a relay having a pair of stationary contacts and a vibrating contact adapted to make alternate connection with the stationary contacts, means for supplying alternating potential to the stationary contacts, means including the vibrating contact for removing direct current, a choke coil connected in series on the output side of the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential, phase-shifting means for shifting the phase between the vibration of the vibrating contact and the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a network having a first resistor and capacitor in series, a second resistor and capacitor in series and a third resistor and capacitor in series, the third resistor and capacitor being connected across a point between the first resistor and capacitor and a point between the second resistor and capacitor and means for varying the relative value of the third resistor with respect to the third capacitor.

4. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a relay having a pair of stationary contacts and a vibrating contact adapted to make alternate connection with the stationary contacts, means for supplying alternating potential to the stationary contacts, means including the vibrating contact for removing direct current, a choke coil connected in series on the output side of the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential, phase-shifting means for shifting the phase between the vibration of the vibrating contact and the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a network having an inductor and a resistor and means for changing the relative value of the inductance of the inductor with respect to the resistance of the resistor.

5. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a relay having a pair of stationary contacts and a vibrating contact adapted to make alternate connection with the stationary contacts, means for supplying alternating potential to the stationary contacts, means including the vibrating contact for removing direct current, a choke coil connected in series on the output side of the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential, phase-shifting means for shifting the phase between the vibration of the vibrating contact and the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a network having an inductor and a resistor and magnetically saturable means for changing the inductance of the inductor.

6. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a transformer having a secondary winding, a relay having a pair of stationary contacts and a vibrating contact, means providing a conducting path between one end of the secondary winding and one of the stationary contacts, means for providing a conducting path between the other end of the secondary winding and the other of the stationary contacts, a pair of output current terminals, means providing a conducting path between one of the output current terminals and an intermediate point of the secondary winding, means including a choke coil providing a conducting path between the other of the output current terminals and the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential of the secondary winding, means for shifting the phase of the vibration of the vibrating contact with respect to the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a capacitor and resistor connected in series across the secondary winding.

'7. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a transformer having a secondary winding, a relay having a pair of stationary contacts and a vibrating contact, means providing a conducting path between one end of the secondary winding and one of the stationary contacts, means for providing a conducting path between the other end of the secondary winding and the other of the stationary contacts, a pair of output current terminals, means providing a conducting path between one of the output current terminals and an intermediate point of the secondary winding, means including a choke coil providing a conducting path between the other of the output current terminals and the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential of the secondary winding, means for shifting the phase of the vibration of the vibrating contact with respect to the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a capacitor and resistor connected in series across the secondary winding and means for varying the relative value of the resistance of the resistor with respect to the capacity of the capacitor.

8. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a transformer having a secondary winding, a relay having a pair of stationary contacts and a vibrating contact, means providing a conducting path between one end of the secondary winding and one of the stationary contacts, means for providing a conducting path between the other end of the secondary winding and the other of the stationary contacts, a pair of output current terminals, means providing a conducting path between one of the output current terminals and an intermediate point of the secondary winding, means including a choke coil providing a conducting path between the other of the output current terminals and the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential of the secondary winding, means for shifting the phase of the vibration of the vibrating contact with respect to the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising an inductor and resistor connected in series across the secondary winding.

9. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a transformer having a secondary winding, a relay 7 having a pair of stationary contacts and a vibrating contact, means providing a conducting path between one end of the secondary winding and one of the stationary contacts, means for providing a conducting path between the other end of the secondary winding and the other of the stationary contacts, a pair of output current terminals, means providing a conducting path between one of the output current terminals and an intermediate point of the secondary winding, means including a choke coil providing a conducting path between the other of the output current terminals and the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential of the secto the resistance of the resistor.

10. Apparatus for inter-converting alternating current to an output current having a direct current component including in combination a transformer having a secondary winding, a relay having a pair of stationary contacts and a vibranting contact, means providing a conducting path between one end of the secondary winding and one of the stationary contacts, means for providing a conducting path between the other end of the secondary winding and the other of the stationary contacts, a pair of output current terminals, means providing a conducting path between one of the output current terminals and an intermediate point of the secondary winding, means including a choke coil providing a conducting path between the other of the output current terminals and the vibrating contact, means for vibrating the vibrating contact at the frequency of the alternating potential of the secondary winding, means for shifting the phase of the vibration of the vibrating contact with respect to the alternating potential through an angle greater than ninety electrical degrees to control the direct current component both in amplitude and polarity comprising a resistor and an inductor connected in series across the secondary winding, means including a saturable reactor for varying the inductance of the inductor and means for controlling the saturation of the reactor.

FRANCIS H. SHEPARD, JR.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,019,608 Dempster Mar. 5, 1912 1,944,756 Quarles Jan. 23, 1934 2,020,681 Garstang Nov. 12, 1935 2,113,762 James Apr. 12, 1938 2,179,337 Leukert Nov. 7, 1939 2,209,806 Bedford July 30, 1940 2,276,784 Koppelmann Mar. 17, 1942 2,322,597 Short June 22, 1943 2,328,264 Doran Aug. 31, 1943 2,354,711 Southgate Aug. 1, 1944 2,358,441 Bowsky Sept. 19, 1944 2,372,966 Kiltie Apr. 3, 1945 2,401,600 Arnold June 4, 1946 2,446,527 Chun et al. Aug. '10, 1948 FOREIGN PATENTS Number Country Date 223,241 Great Britain July 9, 1925 68,702 Sweden Aug. 20, 1928 112,094 Australia Sept. 6, 1939 

